To investigate the mechanism of Gegen Qinlian Decoction in protecting ulcerative colitis(UC) rats by up-regulating the expression of microRNA-542-3p(miR-542-3p).Methods:The SD rats(8～10 weeks) successfully modeled with UC were divided into model group,mesalazine group,and Gegen Qinlian Decoction low-,medium-and high-dose groups,and the same batch of healthy rats with equal weight were used as blank control group,16 in each group.UC affected colon cells were digested and passaged into 24-well plates after entering the logarithmic growth phase,with 2×105 cells per well.The miR-NC,miR-542-3p,anti-miR-NC,and anti-miR-542-3p plasmids were transfected into colonic epithelial cells of UC rats by lip3000 and grouped.The miR-NC and miR-542-3p groups were treated with 10% normal saline for 24 h,while the anti-miR-NC and anti-miR-542-3p groups were treated with 10% Gegen Qinlian Decoction for 24 h.The changes of inflammatory mediators and oxidative stress-related indexes in the cell supernatants were analyzed after treatment.The contents of tumor necrosis factor-α(TNF-α),interleukin-6(IL-6) and interleukin-8(IL-8) in rat colon tissue and cells were detected by enzyme-linked immunosorbent assay(ELISA).The contents of malondialdehyde(MDA),superoxide dismutase(SOD) and glutathione peroxidase(GSH-PX) were detected by chemical colorimetry.Real-time fluorescence quantitative PCR(RT-qPCR) was used to detect the expression level of miR-542-3p.Results:Compared with the conditions in model group,the contents of TNF-α,IL-6,IL-8 and MDA in Gegen Qinlian Decoction high-and medium-dose groups were decreased and the expression levels of SOD and GSH-PX and miR-542-3p were increased(all P<0.05).Compared with UC+miR-NC group,UC+miR-542-3p group had elevated expression level of miR-542-3p,SOD and GSH-PX and lowered contents of TNF-α,IL-6,IL-8 and MDA(P<0.05).Compared with the conditions in UC+anti-miR-NC+Gegen Qinlian Decoction group,the expression levels of miR-542-3p,SOD and GSH-PX in UC+anti-miR-542-3p+Gegen Qinlian Decoction group were reduced,and the contents of TNF-α,IL-6,IL-8 and MDA were increased(P<0.05).Conclusion:Gegen Qinlian Decoction protected UC rats by up-regulating the expression of miR-542-3p,thus eliminating intestinal inflammation.